Generally, a high-voltage DC circuit breaker is a switching device capable of blocking current flowing through a high-voltage power transmission line of about 50 kV or more, such as that for a High Voltage Direct Current (HVDC) system. Such a high-voltage DC circuit breaker functions to block a fault current when a fault occurs in a DC line. Of course, such a high-voltage DC circuit breaker may also be applied to an intermediate voltage DC power distribution system having a DC voltage level of about 1 to 50 kV.
In the case of a high-voltage DC circuit breaker, when a fault current occurs in the system, the fault current is blocked in such a way as to isolate a faulty circuit by opening a main switch. However, since a point corresponding to zero (0) current is not present in the DC line, a problem arises in that an arc occurring between the terminals of the main switch is not extinguished when the main switch is opened, and the fault current continuously flows through the arc, thus making it impossible to block the fault current.
Japanese Patent Application Publication No. 1984-068128, shown in FIG. 1, discloses technology in which a high-voltage DC circuit breaker allows a main switch CB to generate zero (0) current by adding current IDC flowing through the main switch CB to resonant current Ip generated by an LC circuit (Idc=IDC+Ip) and extinguish the arc in order to extinguish the arc occurring when the switch operation of the main switch CB is performed and to block fault current Ic. That is, when the main switch CB is closed, the resonant current Ip is injected to be added to the DC current IDC, and thereafter the resonant current Ip becomes oscillating current due to LC resonance. As the current oscillates along with the main switch CB, the magnitude thereof becomes larger. In this way, negative (−) resonant current (−Ip) becomes greater than IDC, so that the fault current Ic becomes zero current, and then the arc in the main switch CB is extinguished. However, in such conventional technology, resonant current Ip greater than DC current IDC must be added, and thus the actual circuit rating must be more than twice that of the rated current. As a result, a problem arises in that, to generate such a high resonant current Ip, resonance must be performed several times, thus decreasing the blocking speed.